CYA level much more responsive to splashout, temperature, and rain than I had thought

bordelond

Well-known member
Jun 8, 2017
121
New Orleans, LA
What I'm describing here is a problem that's come and gone. A minor problem that didn't even cause us to miss a swim day -- but something that could've grown into much more of a hassle.

Long story short:

- On Friday 6/9/2017, I measured the CYA at 60. Initiated the TFP pool methods in earnest.

- Between 6/9 and 8/2/2017 ... loads and loads of rain. And when it wasn't raining, it was glaring sunlight and daytime temps in the 90s. Nothing but a daily bleach addition throughout all this time (except for one 48 hour period, 7/1-3, where we went out of town, and I 'overchlorinated' beforehand to compensate). Throughout all this time, there were multiple splashout episodes when kids were in the pool ... lowering the level ~3" each time. I counted on rainwater to top it back off later on.

- From late June on, I noticed the pool seeming to need more chlorine in the evenings to stay at the recommended FC/CYA level. I was still dosing as if the pool had a CYA of 60, but I had to go from adding 2 ppm of chlorine in the evening to adding 4 ppm. I chalked it up to sunlight and burnoff.

- 8/3 through 8/17 ... even more rain interspersed with even hotter sunny weather. Anytime it rained, it rained hard and long. No one swam in the pool over these two weeks.

- Friday, 8/18 ... for the first time all summer: cloudiness in the water. Water was crystal-clear all summer long until this date. Raised chlorine to 8 ppm that night.

- Saturday, 8/19 ... swam in the cloudy water, felt the chloramines in my eyes and noticed a chlorine smell. Jumped out later and finally did another CYA test. I was down to a CYA of 30. How long I had been down that low, I have no idea. So, I had confirmation ... my chorine WAS being burned off. At some point, the FC got low enough to give algae (?) just a hint of a foothold -- and they took it.

I immediately added enough liquid stabilizer to raise the CYA to 50. Spent some time stirring it around with a net and keeping it from collecting on the bottom of the pool. Got it good and mixed. I immediately began slamming by adding 7-8 ppm three times during daylight hours and one at nightfall.

Within 24 hours, the pool clarity improved. By yesterday morning, the water looks back to TFP normal -- clear and sparkling. Still keeping the chlorine levels elevated for now, though. Kind of reminds me of taking antibiotics ... gotta keep taking them even after you feel better.

Confession time: There is no skimmer on the pool. I take the net to the pool water all the time and scoop stuff out, big and small. However, I have not once brushed the pool walls or vacuumed the pool. From just about Day One, there has been coffee-ground-sized grit on the bottom of the pool that I can move around, but not really scoop up. Water still looks great, but without a squeaky clean bottom ... the pool can't be called perfect.

...

Oh well. The point of all this was just to post that, depending on temperature, splashing, and rain, CYA levels CAN move down and indirectly cause water issues -- and a lot faster than might commonly be assumed. I loved reading the Pool School articles and learned a ton -- but one of the things I thought I learned was that CYA levels pretty much couldn't go down without significant drainage of a pool. Not so.
 

peirek

Silver Supporter
Jun 21, 2017
538
Sachse, TX
That is a pretty big drop in CYA. Splash out (and subsequent fill water replenshing) along with rain (overflowing pool) will in fact drop the CYA. Temperature will not impact CYA levels. To go from 60 to 30 would require 1/2 your water being replaced. That is a lot! Be sure to pass all 3 tests before ending the SLAM. Pool School - SLAM - Shock Level And Maintain

- - - Updated - - -

It sounds like a vacuum and brushing is in order.....
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
21,276
Laughlin, NV
CYA degradation due to oxidation is real. It is more prevalent for us in the south with high sun angles. Normal oxidation is about 3-5 ppm per month, but I can see 10+ ppm per month loss and I have essentially zero splashout and definitely zero rain!

So it is advisable to test your CYA each month during the summer. I do it monthly (if I am home as we do travel some) each month from April to October. In the winter it is very stable.

Take care.
 

BasicTek

Bronze Supporter
Oct 9, 2016
855
Lake Mary, FL
I had very little splash out but tons of rain and went from CYA of 80 to 60 in less than a month (-25%) I noticed about the same % loss for CH and salt in the same time. That was definitely a bigger loss than expected.

EDIT: I did drain about 3-4 inches of water because the pool was full to the top of the skimmer during that time as well
 

bordelond

Well-known member
Jun 8, 2017
121
New Orleans, LA
To go from 60 to 30 would require 1/2 your water being replaced. That is a lot!
Thinking some more about this: my pool is only 42" deep when totally full (actually overfull, as Intex recommends 39"). The way my Intex pool is set up, the corners are open -- water from a full pool readily splashes out from the corners whenever swimmers are in the pool. Two or three inches is a typical decrease after we've been in the pool (esp when my son's friends have been in it). Three inches of splashout is a about a 7% drop in the volume of the pool. That gets replaced by rain, pool is back to full, water gets splashed out again, etc. That happened at least 10-12 times this summer.

So, it seems like the path to 50% water replacement was fairly direct when looking at it over a period of two and a half months.
 

bordelond

Well-known member
Jun 8, 2017
121
New Orleans, LA
CYA degradation due to oxidation is real. It is more prevalent for us in the south with high sun angles. Normal oxidation is about 3-5 ppm per month, but I can see 10+ ppm per month loss and I have essentially zero splashout and definitely zero rain!
So it's sunlight/oxidation, and not merely air or water temperature, that gets to the CYA. Point taken about monthly CYA testing.
 

peirek

Silver Supporter
Jun 21, 2017
538
Sachse, TX
CYA degradation due to oxidation is real. It is more prevalent for us in the south with high sun angles. Normal oxidation is about 3-5 ppm per month, but I can see 10+ ppm per month loss and I have essentially zero splashout and definitely zero rain!

So it is advisable to test your CYA each month during the summer. I do it monthly (if I am home as we do travel some) each month from April to October. In the winter it is very stable.

Take care.
Learn something new every day on here. Thanks for the knowledge share mknauss! I suspect here in Texas I will see similar results.